1. Field of the Invention
The present invention relates to a triode structure field emission device using carbon nanotubes that is a low voltage field emission material and a driving method thereof.
2. Description of the Related Art
FIG. 1 is a cross-sectional view schematically illustrating the structure of a conventional triode field emission device using a field emission material. As shown in FIG. 1, the conventional triode field emission device includes a rear substrate 1 and a front substrate 10 which face each other having an interval of the length of a spacer 6. Cathodes 2 on each of which a field emission material 5 is formed, gates 3 and anodes 4 are included as electron emission sources between the two substrates. The cathodes 2 are disposed on the rear substrate 1 in parallel strips, and the anodes 4 are disposed on the front substrate 10 in parallel strips to cross with the cathodes 2. The gates 3 are disposed in parallel strips to cross with the cathodes 2 so that they are arranged straightly over the anodes 4. A field emission material 5 and an aperture 3a are formed at places where the cathodes 2 cross with the gates 3. That is, the electron emission materials 5 are coated on the intersections on the cathodes 2, and apertures 3a are formed at the intersections on the gates 3, that is, at the positions on the gates 3 which correspond to the field emission materials, such that electrons emitted from the field emission materials 5 flow into the anodes 4.
As described above, field emission devices have a diode structure made up of cathodes and anodes, or a triode structure in which gates are interposed between cathodes and anodes, such that the amount of electron emitted from the cathodes is controlled. Structures in which carbon nanotubes rather than existing metal tips are applied as electron emission sources formed on cathodes have been recently attempted due to the advent of carbon nanotubes, which serve as a new field emission material. Carbon nanotubes have a large aspect ratio (which is greater than 100), electrical characteristics having conductivity such as conductors, and stable mechanical characteristics, so that they are receiving much attention of research institutions to employ them as the electron emission sources for field emission devices. Diode structure field emission devices using carbon nanotubes can be manufactured by a typical method. However, diode structure field emission devices have a trouble in controlling emitted current, in spite of the easiness of the manufacture, so that it is difficult to realize moving pictures or gray-scale images. Triode structure field emission devices using carbon nanotubes can be manufactured in consideration of installation of gate electrodes right on cathodes and installation of a grid-shaped metal sheet. The former field emission devices has difficulty in coupling carbon nanotubes to cathodes because of the arrangement of gates. The latter field emission devices have problems in that the manufacture is complicated, and control voltage increases.
To solve the above problems, an objective of the present invention is to provide a triode field emission device in which location of gate electrodes under cathodes facilitates the control of emitted current, and it is easy to coat the cathodes with a field emission material, and a driving method thereof.
To achieve the above objective, the present invention provides a triode field emission device including: a rear substrate and a front substrate which face each other at a predetermined gap; spacers for vacuum sealing the space formed by the two substrates while maintaining the gap between the two substrates; cathodes and anodes arranged in strips on the facing surfaces of the two substrates so that the cathodes cross with the anodes; electron emission sources formed on the portions of the cathodes at the intersections of the cathodes and the anodes; and gates for controlling electrons emitted from the electron emission sources, wherein the gates are arranged on the rear substrate under the cathodes, and an insulative layer for electrical insulation is formed between the gates and the cathodes.
Preferably, the gates are formed like a full surface or disposed as parallel strips on the rear substrate to cross with the cathodes so that the gates are located straightly over the anodes.
It is preferable that the electron emission sources are formed on the cathodes at the intersections of the cathodes and anodes, of at least one material selected from the group consisting of a metal, diamond and graphite, or a mixture of the selected material with a conductive material, a dielectric material or an insulative material.
Preferably, the electron emission sources are formed straight on the entire surface or one edge of cathodes at the intersections of the cathodes and gates, and the electron emission sources are formed around at least one hole pierced in the cathodes at the intersections of the cathodes and gates.
In the present invention, the electron emission sources are formed by a method among a printing method, an electrophoretic method and a vapor deposition method. It is also preferable that, when three or more holes are formed, a middle hole is formed to a dominant size, and a field emission material is formed around the outer circumference of each of the holes, so that the uniformity of emission current within a pixel is increased.
To achieve the above objective, the present invention provides a method of driving a triode field emission device including: a rear substrate and a front substrate which face each other at a predetermined gap; spacers for vacuum sealing the space formed by the two substrates while maintaining the gap between the two substrates; cathodes and anodes arranged in strips on the facing surfaces of the two substrates so that the cathodes cross with the anodes; electron emission sources formed on the portions of the cathodes at the intersections of the cathodes and the anodes; and gates for controlling electrons emitted from the electron emission sources, wherein the gates are arranged on the rear substrate under the cathodes to cross with the cathodes so that the gates are located straightly over the anodes, and an insulative layer for electrical insulation is formed between the gates and the cathodes, the method including controlling current flowing between the cathodes and the anodes by controlling the gate voltage.
Preferably, the electron emission sources are formed of at least one material selected from the group consisting of carbon nanotube, a metal, diamond and graphite, on the cathodes at the intersections of the cathodes and gates. Alternatively, the electron emission sources are formed of a mixture of a conductive material, a dielectric material or an insulative material with at least one material selected from the group consisting of carbon nanotube, a metal, diamond and graphite, on the cathodes at the intersections of the cathodes and the gates.
It is preferable that the electron emission sources are formed straight on the entire surface or one edge of cathodes at the intersections of the cathodes and gates.
Alternatively, it is preferable that the electron emission sources are formed around at least one hole pierced in the cathodes at the intersections of the cathodes and anodes.